The invention relates to a valve device for a turbine of an exhaust gas turbocharger which has a valve element for adjusting the charge air pressure that is coupled to a shaft to be actuated thereby.
Modern internal combustion engines are ever more frequently fitted with an exhaust gas turbocharger in order to be able to realize efficient and therefore low-fuel-consumption operation and, at the same time, very high specific power and torque generation of the internal combustion engine. The internal combustion engine can be a diesel engine or a spark ignition engine or some other kind of internal combustion engine.
Such an exhaust gas turbocharger usually comprises a turbine with a turbine wheel and a compressor with a compressor wheel for compressing air which is to be fed to the internal combustion engine. The compressor wheel is driven by the turbine wheel. Exhaust gas from the internal combustion engine is fed to the turbine wheel for this purpose. The exhaust gas drives the turbine wheel as a consequence. By this means, energy contained in the exhaust gas is used for driving the turbine and the compressor and therefore for compressing the engine intake air.
The exhaust gas turbocharger usually includes a valve device associated with the turbine for adjusting the charge-air pressure of the exhaust gas turbocharger. The valve device is usually also referred to as a wastegate and includes at least one valve element, by means of which the charge-air pressure can be adjusted.
The valve element is coupled to a shaft of the valve device, wherein the shaft is used to actuate the valve element. At the same time, the valve element is mounted on a bearing point on a housing element, in particular a turbine housing, of the exhaust gas turbocharger, so that it can be rotated about an axis of rotation relative to the housing element by means of the shaft. When the shaft is rotated about the axis of rotation relative to the housing element, this swivels the valve element about the axis of rotation, as a result of which the charge-air pressure is adjusted.
As an example, the valve element is associated with a bypass channel and serves to adjust a quantity or mass of exhaust gas flowing through the bypass channel. The exhaust gas flowing through the bypass channel bypasses the turbine wheel and, consequently, does not flow to the turbine wheel so that the turbine wheel is not driven by the exhaust gas flowing through the bypass channel. Consequently, neither is the exhaust gas flowing through the bypass channel used for compressing the air, as a result of which the charge-air pressure can be adjusted.
Such a valve device for a turbine of an exhaust gas turbocharger can be found disclosed in US 2003/0196435 A1 for example. The valve element is actuated via the shaft, for example by means of a controller or regulator. Actuating the valve element enables the exhaust gas turbocharger to be matched to different operating points of the internal combustion engine so that, as a result, the internal combustion engine can be operated efficiently and with low emissions.
A reduction in fuel consumption and emissions is continuously aimed for as part of the ongoing development of internal combustion engines. This is also accompanied by the valve element being actuated via the shaft very frequently. It has been shown that this results in an increasing load and therefore an increasing wear on the valve device.
It is therefore the object of the present invention to further develop a valve device of the kind mentioned in the introduction in such a way that the load and the resulting wear on the valve device can be kept particularly low in an easy manner.